Temperature-controlled cabinet

ABSTRACT

A temperature-controllable equipment cabinet comprising a diffusion-absorption refrigeration cycle system ( 5 ), an evaporator pipe ( 4 ) of the refrigeration system extending through a wall ( 9 ) of the cabinet and passing through a sealed enclosure ( 3 ) for containing a heat transfer liquid ( 12 ), the sealed enclosure extending across and forming part of an internal surface ( 15 ) of the cabinet such that the refrigeration system in use extracts heat from within the cabinet to an external environment ( 7 ).

FIELD OF THE INVENTION

The invention relates generally to temperature controlled cabinets usingdiffusion absorption refrigeration cycle systems, in particular relatingto cabinets for containing temperature-sensitive electrical andelectronic equipment.

BACKGROUND

Many items of electrical and electronic equipment have increasedsusceptibility to failure, malfunction or generally accelerateddegradation and shortened lifespan when exposed to large variations intemperature, humidity and other ambient conditions, The problem isparticularly significant for items of equipment that must be left forextended periods of time in environments that are relatively unprotectedfrom atmospheric conditions.

One example is items of control equipment, and in particular, thestandby or backup battery power supplies thereof. Such control equipmentmay be found in power distribution, telecommunication, transport andsecurity systems and may often be situated in isolated and exposedoutdoor and indoor locations. Installing such equipment in an enclosurefor protection from rain or other precipitation can often increasetemperature variations, in that sunlight on the enclosure will tend toheat the contents of the enclosure to far higher temperatures than wouldotherwise be the case. Additionally, in some applications, heat emittingequipment situated close to the sensitive equipment may add to thethermal stress. Thus, there is a requirement to provide cooling or airconditioning to the most temperature sensitive items.

In particular, battery back-up power supplies for power distributioncontrol systems and telecommunication systems in the field have beenobserved to have a service life substantially lower than expectedlargely due to degradation caused by temperature and/or humidityvariation. Solutions in the prior art have provided temperaturecontrolled enclosures for the sensitive equipment ranging from a simpleventilated enclosure through to complete air conditioning systems. Thesesolutions and systems incorporate technologies such as thermoelectricdevices, forced convection, heat pipes, phase change material and vapourcompression cycles.

A problem to be addressed in such temperature controlled enclosures isto make them as thermally efficient as possible, whilst at the same timedeveloping devices that have no moving components which removes the needfor regular and expensive maintenance due to the failure of thosecomponents as a result of mechanical wear and tear. Components which canbe removed include mechanical parts such as fans, pumps and compressorsand consumables such as filters.

An alternative refrigeration cycle or cooling mechanism to those notedwhich can be adapted to be used with electronic and electrical equipmentis the diffusion absorption cycle. This cycle completely avoids the useof mechanical energy and instead it relies on direct thermal energy as apower source. They also use environmentally benign fluids, are reliable,silent and relatively inexpensive to build and have no moving parts.However they have a relatively low refrigeration Coefficient ofPerformance ('COP'), which needs to be improved so that electronic andelectrical equipment such as industrial reserve power batteries canefficiently be cooled.

Inside a conventional temperature controlled enclosure, an evaporatorpipe of the diffusion absorption refrigeration cycle system extendinginto the enclosure has a tendency to cause a build-up of ice when thecooling system is in operation. This introduces safety issues for acabinet containing electrical and electronic equipment. In addition, theability of such a refrigerator system to extract heat from the cabinetis limited because the surface area of the evaporator pipe is typicallysmall when compared to the contents of the cabinet. Simply adding a heatsink composed of a thermally conductive material to the evaporator pipedoes not necessarily solve this problem, because the temperaturedistribution of the heat sink may not be uniform over a large surfacearea.

It is an object of the invention to improve the efficiency of coolingsystems for temperature controlled cabinets.

A further object of the invention is to reduce the variation intemperature throughout the interior of temperature controlledenclosures.

SUMMARY OF THE INVENTION

The invention provides a temperature-controllable equipment cabinetcomprising a diffusion-absorption refrigeration cycle system, anevaporator pipe of the refrigeration system extending through a wall ofthe cabinet and passing through a sealed enclosure for containing a heattransfer liquid, the sealed enclosure extending across and forming partof an internal surface of the cabinet such that the refrigeration systemin use extracts heat from within the cabinet to an external environment.

The sealed enclosure is preferably configured to provide a‘thermo-siphon’ effect, i.e. where a change in density of a workingliquid due to temperature variation is used to generate a pumping forcethrough convention flow, thus improving the distribution of coolingthroughout the enclosure and ensuring that there is no ice build up onthe evaporator pipe coming into contact with any of the contents of theenclosure.

The enclosure may be attached to, or embedded in, the wall by variousmethods which include one or more of gluing, welding and mechanicalfixing. The enclosure through which the evaporator pipe passes may forma part of the ceiling, floor or side wall of the enclosure. The wall mayalternatively be a door of the cabinet. One or more sides of theenclosure may be made of different materials.

The wall of the cabinet preferably comprises a layer of thermalinsulation through which the evaporator pipe extends.

The sealed enclosure is preferably substantially planar in construction,extending across the internal surface of the wall.

The evaporator pipe preferably passes in a horizontal direction throughan upper portion of the sealed enclosure when the cabinet is orientedfor use such that, in use, convective flow of the heat transfer liquidaids heat transfer from within the cabinet.

The invention enables improved temperature controlled enclosures forelectrical and electronic components when used with a diffusionabsorption refrigeration cycle system, leading to lower cost and greaterenergy efficiency and for a wider range of ambient temperatures.

The sealed enclosure forms a thermo-siphon configured through itslocation and shape to optimise and improve convection around theevaporator pipe, thus effectively providing additional surface areaacross which to transfer heat from within the cabinet.

Certain embodiments of the invention can be achieved throughmodification of an existing temperature controllable cabinet through theaddition of a sealed enclosure for containing heat transfer fluid aroundthe evaporator pipe of a diffusion-absorption refrigerator system.

The sealed enclosure may be made from one or a limited number of piecesof material, which improves the ease of manufacture of the enclosure andthe ease of installation around the evaporator pipe.

Preferred embodiments of the invention require no moving parts, such asfans which would increase the maintenance costs of the equipment. Heattransfer from the evaporator pipe is instead effected without forcedconvection. Ice build-up around the evaporator pipe is also prevented,enabling electrical and electronic components within the cabinet to besafely cooled, and the temperature distribution within the cabinet mademore uniform. Additional fans may, however, be used where increased heattransfer is required, though at the expense of additional maintenancecost and complexity.

DETAILED DESCRIPTION

The invention will now be described by way of example, and withreference to the appended drawing in FIG. 1 which shows across-sectional view of a diffusion-absorption refrigeration system.

With reference to FIG. 1 a diffusion absorption refrigeration system 5is attached to a structural part of a cabinet, for example beingattached to a door or a wall 9 of the cabinet. The wall 9 comprises alayer of insulation 10 to thermally isolate the internal volume 8 of thecabinet from the external environment 7.

A recess 14 is provided in the wall 9, for example within the layer ofinsulation 10, through which the evaporator pipe 4 passes. The recessallows the wall 9 to be kept relatively thin without unduly compromisingthe insulation of the internal volume 8 of the cabinet. The recess alsoallows the evaporator pipe 4 to be offset from other warmer parts of thesystem.

The evaporator pipe 4 of the refrigerator system 5 acts to draw heatfrom within the cabinet, and a heatsink 11 attached to the condenser ofthe system 5 conducts this heat to the external environment 7.

A liquid-filled enclosure, or thermo-siphon 3, is attached to the insideof the wall 9, forming a sealed vessel surrounding the evaporator pipe4. The enclosure 3 comprises one or more filling points for introducingliquid 12 into the enclosure once it has been fixed in place around theevaporator pipe 4. The liquid filled enclosure 3 may be attached to thestructural insulation 10, or to a material enclosing the insulation, byway of welding, gluing or other mechanical fixing methods, for exampleat fixing points 2 a, 2 b on the edge of the enclosure 3.

The enclosure 3 may have one or more sides or faces in common with thestructural insulation 10 or a material enclosing the insulation, forexample along an interface 13 between the internal volume of theenclosure 6 and the insulation 10. The external surface 15 of theenclosure 3 may be in direct contact with the contents of thetemperature controlled enclosure, or may act as a cooling element acrossthe internal wall 15 for cooling air within the cabinet.

The size of the thermo-siphon is preferably optimised to provide abalance between thermal efficiency in heat transfer, cost ofmanufacture, fit with the refrigeration cycle and weight of fluid. Theembodiment shown illustrates a particular preferred embodiment, wherethe enclosure 3 is in a substantially planar form extending across theinternal surface of the wall, so as to maximise the cooling effectwithin the cabinet and minimise the quantity of heat transfer liquidrequired.

Preferably, the evaporator pipe 4 is located towards an upper end of theenclosure 3, extending through the enclosure in a substantiallyhorizontal direction. The upper location of the pipe 4 allows for theconvection effect to be optimised, since cool liquid within theenclosure 3 in contact with the evaporator pipe 4 will sink away fromthe pipe 4. As the liquid 3 absorbs heat from the internal volume 8 ofthe cabinet, the liquid rises and is then cooled again by the evaporatorpipe 4, creating a convection cycle between the evaporator pipe 4 andthe bottom of the enclosure 3. Any volume of liquid above the evaporatorpipe 4, however, is not able to contribute to the convection cycle, dueto a thermocline being set up within the liquid 12 around the level ofthe evaporator pipe 4. The evaporator pipe 4 therefore preferably passesthrough an upper portion of the enclosure 3, and more preferably as nearto the top of the enclosure as practical, so as to maximise theefficiency of the thermo-siphon effect.

Testing has indicated that a typical temperature difference ΔT betweenthe contents of a temperature controlled enclosure, for example in theform of industrial batteries, and the external ambient environment ofonly around 15° C. can be achieved using standard 80 W diffusionabsorption cycle refrigeration systems. In addition, the temperature ofthe contents of such a cabinet can vary by over 10° C. between the topand the bottom of the cabinet. Using the modifications to the cabinetdescribed herein, this variation can be reduced to below 5° C. Theinvention also enables the refrigerator system to be used in elevatedambient temperatures (well above ‘domestic room’ temperatures) of up to60° C., while maintaining the contents of the cabinet below 50° C. andwith a reduced variation of temperature within the enclosure. Aneffective minimum ΔT of 15° C. can be maintained for the contents of thecabinet down to around room temperature ambient (around 20-25° C.).

Because the equipment cabinet is required to be thermally isolated fromthe external environment, a vent may be added to the cabinet to ensurethat noxious or explosive gases (such as hydrogen) are dissipated to theexternal environment, thus avoiding any explosive build up of gas withinthe cabinet, which could be generated during operation of the equipmenttherein.

Other embodiments are intentionally within the scope of the invention,as defined by the appended claims.

1. A temperature-controllable equipment cabinet comprising adiffusion-absorption refrigeration cycle system, an evaporator pipe ofthe refrigeration system extending through a wall of the cabinet andpassing through a sealed enclosure for containing a heat transferliquid, the sealed enclosure extending across and forming part of aninternal surface of the cabinet such that the refrigeration system inuse extracts heat from within the cabinet to an external environment. 2.The equipment cabinet of claim 1 wherein the wall of the cabinetcomprises a layer of thermal insulation through which the evaporatorpipe extends.
 3. The equipment cabinet of claim 2 wherein the evaporatorpipe passes through a recess provided in the wall.
 4. The equipmentcabinet of claim 3 wherein the sealed enclosure is substantially planarin construction across the internal surface of the wall.
 5. Theequipment cabinet of any preceding claim 4 wherein the evaporator pipepasses in a horizontal direction through an upper portion of the sealedenclosure when the cabinet is oriented for use such that, in use,convective flow of the heat transfer liquid aids heat transfer fromwithin the cabinet.
 6. (canceled)
 7. The equipment cabinet of claim 1,wherein the evaporator pipe passes through a recess provided in thewall.
 8. The equipment cabinet of claim 7 wherein the sealed enclosureis substantially planar in construction across the internal surface ofthe wall.
 9. The equipment cabinet of claim 8, wherein the evaporatorpipe passes in a horizontal direction through an upper portion of thesealed enclosure when the cabinet is oriented for use such that, in use,convective flow of the heat transfer liquid aids heat transfer fromwithin the cabinet.
 10. The equipment cabinet of claim 1 wherein thesealed enclosure is substantially planar in construction across theinternal surface of the wall.
 11. The equipment cabinet of claim 10,wherein the evaporator pipe passes in a horizontal direction through anupper portion of the sealed enclosure when the cabinet is oriented foruse such that, in use, convective flow of the heat transfer liquid aidsheat transfer from within the cabinet.
 12. The equipment cabinet ofclaim 1, wherein the evaporator pipe passes in a horizontal directionthrough an upper portion of the sealed enclosure when the cabinet isoriented for use such that, in use, convective flow of the heat transferliquid aids heat transfer from within the cabinet.
 13. The equipmentcabinet of claim 1 wherein the heat transfer liquid includes a mixtureof water and glycol.